Feline immunodeficiency virus (FIV)

FIV (feline immunodeficiency virus) is a viral infection which affects cats. It was first discovered in domestic cats in 1986 and since then it has been discovered that it is endemic across the world. FIV not only affects domestic cats but also wild cats. For example FIV is endemic in African lions and it has been diagnosed in cheetahs. FIV is very similar to the human immunodeficiency virus (HIV) and when it was first discovered in cats there was panic at the thought of people being made HIV positive by their pets. It is now known that FIV is genus-specific - which means that it cannot be transmitted to humans, dogs or indeed any animals apart from other cats.

The science of FIV

FIV infects cells of the immune system (that part of the body responsible for defense against infection and tumours). FIV attacks CD4+ T cells, CD8+ T cells, B cells, dendritic cells and macrophages, that is, any cells which are part of the immune system. Because FIV is a lytic virus, it will kill infected cells and so destroy the immune system. Although FIV itself does not kill cats, it makes them cat vulnerable to other infections and cancer.

The disease has three stages :

  1. Early infection - the cat may have a temperature, poor appetite and appear lethargic. This is because the virus is multiplying very rapidly and the viral load in the cat's body is high. At this stage the immune system still functions and it fights back by developing anti-viral antibodies. These eliminate a large amount of the virus, and as the viral load decreases the cat appears to return to normal. But the FIV is still lurking in its system.

    One of the major problems with FIV is that the virus mutates in order to avoid the immune system response making it very hard to destroy.

  2. As long as the system can produce antibodies the virus will be kept in check - this is the so-called latent stage. This can last for months or years with the cat showing no symptoms of the illness. However, it remains FIV positive and infectious to other cats. As the virus slowly kills off immune cells the system's responses become weaker and weaker and eventually the disease will move into its final phase.

  3. The chronic stage develops when the immune system is too weakened to cope with opportunistic infections. These can include: stomatitis, odontoclasia, periodontitis, gingivitis, rhinitis, conjunctivitis, pneumonitis, enteritis, and dermatitis. (Infections of the mouth, nose, eyes, lungs, intestines and skin) These secondary diseases are what actually kill the cat.

About the virus

FIV is a Lentivirus of the Retroviridae family. Viruses in the Retroviridae family are enveloped RNA viruses in which replication involves a DNA stage. That is, the viruses manage to insert themselves into the infected animal's DNA. Scientists explain that to do this, the retroviruses perform so called reverse transcription of its genome to turn the RNA into DNA which can then be integrated into the host's DNA. There are two enzymes which are involved in this process: reverse trascriptase which turns RNA into DNA and integrase - an enzyme which integrates the viral DNA into host DNA. Once inside the host DNA, viral DNA is transcribed like any other host DNA using host RNA polymerase an enzyme which transcribe DNA into a full-length RNA. Lentiviruses (from Latin 'lenti-" meaning 'slow') are retrovirus which take a long time to do their damage.


There are a number of tests for FIV and most vets can do them at their surgeries:

ELISA - enzyme-linked immunosorbent assay - detects anti-FIV antibodies in infected animals. This is rapid and reliable method is most commonly used. ELISA kits available on the market detect antibodies against a viral core protein (p24) or/and transmembrane envelope protein. (gp40). Because this technique relies on detecting of antibodies, it does not work well with very early infections since it takes approximately 4 to 8 weeks for the cat's body to develop antibodies. False positives are rare but they can happen. Consequently ELISA positive tests are generally repeated to be sure.

Immunoblotting also detects antibodies to a HIV related proteins. In this method the proteins are septed on and agarose gel by elecrophoreses. The proteins are than transferred onto nitrocellulose paper simply by diffusion through pressure. The nitrocellulose is then incubated with serum sample to detect the antibodies.

PCR (polymerase chain reaction) - PCR detects the virus itself. This makes very useful for detecting infection in kittens from an FIV positive mother, since anti-FIV antibodies are passed from the infected mother to her kittens and therefore antibody-based tests are unreliable. It can also check for false positives - for example in healthy cats with no prior contact with an FIV infected animal.

How is FIV spread?

FIV is spread mainly through bites. So unspayed males which regularly get into fights are more at risk. Cats living with a non-aggressive FIV infected cat are less at risk, although about 2% may become infected, mainly through saliva when cats share their food and water bowls. FIV infected mothers infect approximately 1 in 5 of their kittens.

How can I protect my cat from FIV infection?

Since the main route of transmission is through bites it is important to prevent cat fights as much as possible. Being less aggressive, neutered cats get into trouble less. Indoor cats too, are much less at risk. If you allow your cat outdoors, keep her in during the night. Although all cats can be infected, older or already sick animals are likely to progress to the chronic phase much quicker.


There is no treatment for FIV therefore helping an infected cat to live longer will depend on proper health management. See our section on living with an FIV infected cat. Remember, the secondary infections (which is what kills the cat) can be sucessfully treated. Also healthy FIV-positive cats should be vaccinated normally to boost their immune systems and given the usual treatment against psites.


A vaccine for FIV has been licensed in the USA , but it is not certain how effective this is in the real world. It certainly does not work against all subtypes of FIV and makes testing difficult, since there is no way to distinguish between vaccinated and infected animals. The vaccine is not available in the UK .

Living with an FIV-infected cat

It is important to stress that FIV infected cats often live a nearly normal life span. Many FIV infected cats are often unnecessarily euthanized. Naturally, owners have to be more vigilant for early signs of infection, an FIV infected cat should be kept indoors - both for her own protection and to protect other cats. Minimizing the risk of casual infection is the key to a happy life for a FIV cat.

Of course is is better if the FIV cat does not share a house with other cats, but a well managed multi-cat household has minimal risk to the other cats. The important thing is to keep food bowls, water and cat litter septe. A transmission through casual contact appears to be extremely rare if it happens at all. It is therefore not essential to quarantine an FIV infected animal unless it is likely to bite its housemates.

Uncooked meat should be avoided it can carry bacteria and some psites. Regular visits to the vet are required to check for early signs of illness and for regualr vaccinations and anti-psite treatments.

Note: This information is for guidance only. It is not intended to replace consultation with a licensed practitioner.

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